Microsurgical instruments, for example retractors, are often designed to be able to be dismantled, so as to be able to be more easily cleaned. The shaft, the handle and the retraction structure, or another working structure, can be separable from one another. It is known for the connection between the shaft and the retraction structure, or the other working structure, for example a tool head, to be produced by a releasable coupling device such as a bayonet catch.
DE 10 2006 038 516 A1 discloses a tubular shaft instrument with an actuation rod which is guided in a shaft, and of which the proximal end can be connected to an actuation element, and of which the distal end is coupled to the tool head for actuating the tool.
A sleeve lies on the tool head and is releasably coupled to the hollow shaft via a pin-and-slot connection with a curved guide track.
Although pin-and-slot connections or bayonet connections have the advantage of being able to be operated intuitively and quickly, they tend to come apart automatically under a torsional load, which poses a safety risk especially in the case of tool heads of considerable weight or tool heads with considerable radial projection, such as a retraction structure. Attempts were therefore made to seek solutions that would make accidental release of the bayonet connections more difficult.
A bayonet connection of this kind, provided for connecting two tubular instrument parts, is disclosed in DE 197 07 373 C1. There, on a distal half of the instrument, a bayonet sleeve is provided which has an L-shaped slit, wherein a bayonet insert, with engagement lugs protruding radially and along the longitudinal axis, is inserted into the bayonet sleeve. Arranged distally “behind” the bayonet sleeve is a locking piece which is pressed in the proximal direction by a spring and, on its end face, has a recess whose shape corresponds to the lugs of the bayonet insert. When the bayonet insert is located in its rotation-locking position, the lugs engage in the recess and the locking piece springs back, as a result of which further rotation of the bayonet insert is suppressed. While the solution proposed there makes rotation more difficult, it does not entirely prevent it, since, if the torque on the shaft is high enough, the locking piece can be moved counter to the spring load, as a result of which the engagement with the recess is canceled.
Further modified bayonet connections were therefore developed that were intended to more reliably suppress any accidental rotation.
Thus, DE 10 2012 007645 relates to a joint device for a medical instrument in which a handle, by way of a shaft, is coupled to a joint by means of a bayonet. An actuation rod and an inner shaft, which are provided for the operation of tool functions, are provided in the shaft. The (outer) shaft is connected to a joint body via the bayonet connection. For this purpose, a sleeve, with radially protruding claws at its proximal end, is arranged on the proximal end of the joint. The sleeve has a longitudinal axial slit through which a radially protruding cam, secured in a fixed position on the inner shaft, emerges. This cam has a greater length and extends radially farther than the sleeve is thick. The cam can be brought together with the inner shaft to a distal end position in which it is received on the joint body in a corresponding niche of a flange of the sleeve. At its distal end, the (outer) shaft has an L-shaped slit which is pulled over the sleeve of the joint body for the coupling, wherein the claws are brought into engagement with the slit.
The longitudinal axial slit portions and the niche of the flange, in which the cam is received, are aligned in the locking position of the bayonet, such that the cam can be moved out of the niche in the proximal direction into the longitudinal axial slit portions, as a result of which an anti-rotation means is achieved. There, however, the anti-rotation means can become effective only when the cam is moved out of the niche and is in engagement with the two longitudinal axial slit portions.